To ensure trouble-free operation and to utilize the full output potential of a turbo generator, large generators must be cooled in order to dissipate the heat loss which occurs in the windings and cores of the rotor and stator. A fluid such as air or even hydrogen is generally used for the cooling and is fed through corresponding bores or slits in the rotor and stator and then cooled down again in a cooler.
In the rotor, the cooling medium flows axially from the ends into corresponding bores of the rotor conductor toward the inside, issues radially into the air gap between stator and rotor after absorbing the rotor heat loss, and can then flow either axially in the air gap outward, or radially through cooling channels in the stator core.
The laid open German patent application DE 40 11 450 A1, which is incorporated by reference herein, describes a simple radial cooling scheme for a rotor winding of a turbo generator. According to this disclosure, the cooling gas enters the rotor winding via a sub slot which is machined below the main winding slot. The gas then passes radially outwards through ventilation holes in the winding conductors to the air gap of the machine. According to this scheme, the radial holes are inclined in order to achieve a better flow condition within the cooling channels and improve the cooling compared to pure radial flow machines.
Other cooling schemes describe the use of one or more inner channels within the conductor. A cooling medium passes through these channels axially for a certain distance before exiting the conductor. The inlets and outlets to and from these axial sections are generally formed by radial cooling ducts similar to pure radial cooling schemes.
The German laid open patent DE 1 036 370, related to U.S. Pat. No. 2787721, both of which are hereby incorporated by reference herein, describes a cooling scheme wherein each conductor has a single axial duct. The cooling medium passes through these single axial ducts. In this case, the cooling medium, generally gaseous air or hydrogen, is fed to the conductor stack in the slot portion from a sub slot machined below the main winding slot. The gas then passes axially along the conductors in both the forward and reverse direction based on the flow direction in the sub slot. After a certain distance the gaseous medium exhausts radially into the air gap.
The German laid open patent DE 1 120 575, which is incorporated by reference herein, describes a similar cooling scheme with each conductor having two axial ducts for the flow of the coolant. Each axial duct is fed in a way similar to that described for DE 1 036 370. The arrangement of the radial gas inlets and outlets to each axial duct is axially offset such that a cross flow arrangement in adjacent ducts is achieved. This cross flow scheme serves to reduce the temperature hotspots within the conductor closer to that of the average conductor temperature for that section of the winding.